Scientists Explain: Why Humans Have an Appendix — And What Evolution Says About This Puzzling Organ

Vestigial structures refer to anatomical features that humans and other living organisms possess that have lost their original functionalities due to evolution, but are still currently present at reduced size or complexity. Charles Darwin argued that humans’ appendix was one of those vestigial remnants that lost their utility over millions of years.

However, most people still ask why we still have them if we no longer need these organs, or how we came to not need them anymore. This is a question that will be answered through understanding the Appendix’s original functions, that was taken away by human evolution and adaptation.

Once Used to Digest Plants

Charles Darwin proposed that the human appendix is a product of a larger digestive organ, the cecum. However, it is now a vestigial remnant and is not essential for the survival of a human being, unlike other organs.

He argued that our ancestors used to break down tough plant material as their main diet millions of years ago. Appendix is especially useful during this time as to process and digest those plants, the larger organ we used to have is more effective for this specific food source.

But, as our diets shifted to softer and more easily digestible foods like fruits and cooked meat, the cecum shrank over countless years. However, the appendix remained and became a leftover structure that we can survive without.

Read more: Science Daily

A “Safe-House” for Gut Bacteria

The Appendix: Evolution’s Biggest Mystery Revealed!

Some evolutionary biologists confirm that the appendix evolved independently at least 30 times across different animals, such as humans, apes, rodents, koalas, and others. It means it is not unique to humans, and is probably an important structure a long time ago in these living organisms that once served a digestive or immune function.

There are good bacteria in our digestive system that play various roles crucial for the organ to do its job. Recent studies show that the appendix is rich in lymphoid tissue and appears to have a healthy amount of beneficial bacteria.

Which means that after the removal of those bacteria, either due to infection or antibiotics that we often use to take nowadays, they can help repopulate the digestive tract with good microbes, therefore reducing the risk of reinfection. In other words, it is not totally useless, but we could still survive without it.

Vestigial or Functional? It’s Complicated

An organ could be vestigial, but still functional. However, more often than not, their importance is reduced, and most living organisms could live even if they were removed from their bodies. But due to those modern studies, it has now become more complicated.

We now understand that they could still serve a minor functionality in our immune system, and we also can’t ignore the fact that they have persisted for a very long time, estimated to be over 80 million years.

These signs indicated that evolution and natural selection heavily favored the existence of this organ, and not only in humans but across species as well. It might not be essential for survival, but there’s also a possibility that it still holds significance that we just do not understand yet.

Read more: The Scientist

What It Reveals About Human Evolution

The presence of the appendix showcases how evolution could repurpose structures, turning an organ that was once part of a larger digestive system into an immunity asset. It also tells us that vestigial organs are not always useless, or will remain useless for their whole existence in the population.

They might retain or even develop new functionalities that could help our bodies survive, through the same process that made them less relevant, evolution. Ultimately, the existence of our appendix is complex and will require further studies, both in our past and future, to completely understand.

Why Your Appendix Actually Matters

Author's Final Thoughts

The appendix is thought to have begun as a digestive tool for a heavy plant-based diet that requires a larger organ named the cecum. Based on present studies, it is now repurposed into an immune reservoir for beneficial gut bacteria.

This is a shift that highlights how evolution could be both adaptable and resourceful. It should also remind us that vestigial remnants of our past persisted for many years, and that it was a part that was naturally selected through evolution, and should not just be instantly labeled as useless.

Read more: Scientists Confirm the Oldest Rock on Earth Is 4.16 Billion Years Old — And It’s in Canada

References & Further Reading

Smith, H. F., & Parker, W. (2023). A review of the function and evolution of the cecal appendix. The Anatomical Record. https://anatomypubs.onlinelibrary.wiley.com/doi/10.1002/ar.24917

Kooij, I. A., Sahami, S., Meijer, S. L., Buskens, C. J., & te Velde, A. A. (2016). The immunology of the vermiform appendix: a review of the literature. Clinical & Experimental Immunology. https://doi.org/10.1111/cei.12821

Bollinger, R. R., Barbas, A. S., Bush, E. L., Lin, S. S., & Parker, W. (2007). Biofilms in the large bowel suggest an apparent function of the human vermiform appendix. Journal of Theoretical Biology. https://doi.org/10.1016/j.jtbi.2007.08.032

Collard, M. K., et al. (2021). The cecal appendix is correlated with greater maximal observed longevity in mammals. Journal of Anatomy. https://pmc.ncbi.nlm.nih.gov/articles/PMC8546507/

Collard, M. K., et al. (2023). Correlation between the presence of a cecal appendix and reduced risk of severe diarrhea in primates. Scientific Reports. https://www.nature.com/articles/s41598-023-43070-5